The most direct route for converting chlorinated phthalic anhydrides to corresponding fluorinated compounds involves direct fluorination of the chlorinated anhydrides. Attempts at direct fluorination of tetrachlorophthalic anhydride (hereafter sometimes referred to as "TCPAN") have been reported in Odinokov, V. N. et al, Zh. Obshch. Khim., 37(1), 176-181 (1967) as follows. When TCPAN was heated with potassium fluoride in boiling dimethylformamide, no tetrafluorophthalic anhydride was said to be obtained; the only product identified was octafluoroanthraquinone produced in 2% yield. When TCPAN was heated with anhydrous KF at 300.degree. C. in the absence of solvent, octafluoroanthraquinone was said to be obtained in 40 to 45% yield and tetrafluorophthalic anhydride is not mentioned as a product. Furthermore, the inventors herein have tried the direct fluorination of TCPAN using the most recent advances in KF technology. The reaction was run in acetonitrile at 83.degree. C. in the presence of a mixture of phase-transfer catalysts; the main products were dilactones and the yield of tetrafluorophthalic anhydride was only 1.4%.
It is an object herein to convert chlorinated phthalic anhydrides to fluorinated product without dilactone formation.